Magnetic holding device

ABSTRACT

A magnetic cylinder or section of a magnetic cylinder comprises a layer of ferromagnetic material inserted between separate sections of the ferromagnetic material.

United States Patent 1191 1111 3,810,055 Wri ht 1451 May 7, 1974 [54] MAGNETIC HOLDING DEVICE 3,643,311 2/1972 Knechtel et a1. 101/382 MV 3 616145 10/1971 Clifton ....335/303 X [76] Inventor: Theodore D. Wright, 511 Grand 3624731 H 971 Hill, St. Paul, Minn. 55102 H 0 I v [22] Filed: May 1 Primary Examiner-George Harris [21] Appl, No.1 361,898 Attorney, Agent, or Firm-Marvin Jacobson [52] US. Cl 335/285, 101/382 MV 51 Int. Cl. ..n01r 7/20 [.57] ABSTRACT [5 8] held of Seal-ch 3 8 A magnetic cylinder or section of a magnetic cylinder 33 8 3 comprises a layer of ferromagnetic material inserted 1 th f 56] References Cited I :ztlyveen separate sectlons o e erromagnenc mate UNITED STATES PATENTS 3,742,852 7/1973 Leffler et a]. 335/306 X 5 Claims, 2 Drawing Figures MAGNETIC HOLDING DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is intended for use as a curved surface magnetic latch or holding device, specifically in the form of a magnetic cylinder or a section of a magnetic cylinder. Although the invention will find use in other areas, its principal importance is for use in conjunction with and for holding curved steel-backed ferromagnetic printing plates duringthe printing operation.

2. Description of the Prior Art Prior art magnetic cylinders have been constructed with permanent bar magnets indented in the surface of the cylinder. Also, some magnetic cylinders have been constructed with permanent magnet rings around the cylinder spaced across the length of the cylinder. The instant invention is an improvement over these types of magnetic cylinders in that the desired holding strength of the magnetic field is attained with improved construction features so that the cylinder is easier and cheaper to manufacture. The magnetic cylinder constructed according to the teachings of this invention lends itself more readily to automated and mechanized manufacturing techniques.

SUMMARY OF THE INVENTION A layer of ferromagnetic material is supported on a layer of nonmagnetic'material and there are slots or gaps through the layer of ferromagnetic material which are filled with strips of flexible, permanently magnetized material with the latter arranged and polarized so that each separate portion of the ferromagnetic layer serves as a pole piece for a magnetic field path in conjunction with the next adjacent portion of ferromagnetic layer. Preferably, the slots between the portions of ferromagnetic material spiral around the cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view of a preferred embodiment of the invention; and

FIG. 2 is a sectional view of FIG. 1.

Referring to the drawings, the magnetic cylinder has an inner layer 10 made of aluminum or other suitable nonmagnetic material. This provides a physical support for the ferromagnetic material without providing a low reluctance path for the magnetic flux lines. Layer l may constitute the core of the cylinder or may be part I I of a solid or hollow core. In some suitable fashion, not

constituting a novel aspect of the invention, the cylinder is provided with a drive shaft 11. Around the aluminum core 10 is a layer 12 of ferromagnetic material such as hardened steel. Passing completely through the thickness of the steel layer 12 are a series of slots or gaps 13 so so that the ferromagnetic layer 12 actually consists of a group of parallel and separate sections of ferromagnetic material supported on the nonmagnetic layer I0. Between each section or portion of the ferromagnetic layer 12 in each of the gaps I3, there is inserted a strip 14 of permanent magnetic material. In the embodiment the outside surface of the permanent magnetic material strip 14 is slightly below the outer surface of the ferromagnetic layer 12 so that a slight recess or depression is formed. The reason for this is that it has been found preferable that the article being magnetically held in place on the cylinder make contact with the ferromagnetic layer rather than the permanent magnet material in order to prevent wear or other dam age to the latter. In most instances it is preferable that this recess be filled with some hard inert material to serve as a protective layer and to prevent any dirt or grime from settling in the recess. Also this then provides the magnetic cylinder with a smooth and even outer surface which may be desirable. However, it is contemplated that if a more durable substance is used for the permanent magnet material, then this protective feature would no longer be necessary. It is also contemplated that protection against wear can be achieved by coating the entire surface of the cylinder with a thin layer of some suitable protective material without substantially affecting the magnetic holding strength. This would also eliminate the need for the recess.

The strips 14 of permanent magnetic material which are inserted in each of the slots 13 are polarized with magnetic north on one side of the material and magnetic south on the other side. As illustrated in FIG. 2, each section of ferromagnetic layer 12 has the same magnetic pole on each side and each next adjacent ferromagnetic section 12 is oppositely polarized. In the illustration shown in FIG. 2, it can be seen, starting from right to left, that each section of the ferromagnetic layer 12 is alternately polarized south and north. These sections then constitute pole pieces for the magnetic paths produced by the strips 14 of permanent magnetic material which are located in each of the gaps l3 between'each of the sections of the ferromagnetic layer 12. In this fashion, each of the ferromagnetic sections then is polarized so that the continuous lines of magnetic force pass through air from each of the respective pole pieces to the next adjacent pole piece. In the well-known manner, then, the lines of force which pass through the air in that fashion provide the magnetic force to attract and hold any ferromagnetic article such as, for example, a steel-backed printing plate saddle or similar article.

The gaps 13 shown in the illustrated preferred embodiment comprise a pair of parallel slots which spiral around the outer surface of the cylinder. In this fashion, then, two strips of permanent magnetic material arranged in the correct polarity, as illustrated, can then be wrapped around the cylinder inserted in the respective slots.

Typically, the cylinder can be manufactured by first slipping a ferromagnetic steel sleeve tightly over a solid or hollow core made of aluminum or some other nonmagnetic material and then bonding the two together solidly in some fashion. The cylinder is then machined to produce the parallel slots spiraling around the outside of the cylinder with the slots being cut completely through the ferromagnetic layer so that there is no closed magnetic path between adjacent sections of the ferromagnetic layer. Next, a flexible strip of permanent magnet material is wound around the cylinder in one of the spiral slots and a separate strip of flexible permanent magnetic material is wound around the cylinder inserted in the other spiral slot. Of course, both strips can be wound around the cylinder and inserted in their respective slots at the same time. In any event, these strips must be properly magnetically oriented so that the correct magnetic poles appear in juxtaposition with 1 each of the sections of the ferromagnetic layer. By means not shown, which do not constitute a novel part of the invention, the magnetic material strips are firmly bonded to the nonmagnetic core and the ferromagnetic layer to insure that they are held securely in their positions during use. A suitable adhesive that can be used for this purpose is an epoxy resin such as the commercial product known as Fullers Resiweld FE-7004. Finally, it is preferable that if the cylinder is made with recesses in the outer surface that-they be filled with some suitable hard, inert material. This may be, for example, an aluminum filled epoxy such as the commercially available product known as Minnesota Mining Structural Adhesive I75 I.

The preferred material for the strips 14 of flexible permanent magnet is a rubber-bonded, barium ferrite composite material which is known commercially under the registered trademark name of Plastiform" and is made by Minnesota Mining and Manufacturing Company. This material has the characteristic of being flexible enough to be bent or twisted or wound in a variety of shapes or forms and consists of a rubber based matrix or binder containing powdered ferrite particles which are mechanically orientated during .processing and aligned andheld to constitute a good permanent magnet. Because a flexible permanent magnet material is used, it lends itself to certain manufacturing advantages because it can be easily wrapped around the cylinder and inserted in the spiral slots by automated mechanical means after the slots have been machined in the cylinder.

A magnetic cylinder formed in the manner described can then be cut or severed into sections which then can be used as individual saddles or the like for use in printing or other types of operations requiring a curved magnetic holding surface.

I claim:

1. A device for providing an external magnetic holding force, comprising: a curved layer of unmagnetized ferromagnetic material having a constant radius of curvature supported on a layer of nonmagnetic material; a pair of parallel spiral slots passing completely through said ferromagnetic layer forming said ferromagnetic layer into two spiralling parallel separate sections; a strip of permanently magnetized material contained in each slot in contact with each adjacent ferromagnetic section, the strips being arranged and polarized so that each ferromagnetic section has the same magnetic pole juxtaposed on each of its two sides and alternate sections are oppositely polarized whereby said ferromagnetic sections comprise oppositely polarized magnetic pole pieces. I

2. A magnetic device as described in claim 1 wherein the curved layer is in the form of a cylinder.

3. The magnetic cylinder as described 'in claim 1 wherein each strip of permanently magnetized material is flexible when inserted inthe slots.

4. The magnetic cylinder as described in claim 2 wherein each strip is continuous and is permanently magnetized with a north pole on one side and a south pole on theother side along the entire length of the strip.

5. The magnetic cylinder as described in claim 4 wherein one strip of permanently magnetized material is contained in one of the slots and a separate strip is contained in the other slot. 

1. A device for providing an external magnetic holding force, comprising: a curved layer of unmagnetized ferromagnetic material having a constant radius of curvature supported on a layer of nonmagnetic material; a pair of parallel spiral slots passing completely through said ferromagnetic layer forming said ferromagnetic layer into two spiralling parallel separate sections; a strip of permanently magnetized material contained in each slot in contact with each adjacent ferromagnetic section, the strips being arranged and polarized so that each ferromagnetic section has the same magnetic pole juxtaposed on each of its two sides and alternate sections are oppositely polarized whereby said ferromagnetic sections comprise oppositely polarized magnetic pole pieces.
 2. A magnetic device as described in claim 1 wherein the curved layer is in the form of a cylinder.
 3. The magnetic cylinder as described in claim 1 wherein each strip of permanently magnetized material is flexible when inserted in the slots.
 4. The magnetic cylinder as described in claim 2 wherein each strip is continuous and is permanently magnetized with a north pole on one side and a south pole on the other side along the entire length of the strip.
 5. The magnetic cylinder as described in claim 4 wherein one strip of permanently magnetized material is contained in one of the slots and a separate strip is contained in the other slot. 